Pocketed coil springs, ie strings of springs enclosed within fabric pockets which are joined at their side seams, are widely used in the manufacture of mattresses, cushions and the like.
Apparatus for the production of pocketed coil springs may generally be regarded as comprising two sections: a coiling unit in which the coil is formed and an encapsulation section in which the coil is inserted between two layers of material which are then joined together to form a pocket enclosing the spring.
The coiling of the wire is commonly achieved by the interaction of three components: feed rollers which pull the wire through the coiler, a so-called “finger” which governs the diameter of the spring as it forms and a so-called “spreader” which controls its pitch. The relative movements of these components define the pattern of the spring that is formed.
Conventionally, synchronisation is achieved by a complex arrangement of gears and cams, making resetting between one product and another a lengthy operation needing high levels of training and experience. Consequently, economic batch quantities are high and response to special customer requirements is slow. Development of new spring designs is difficult, often relying on the creation of new cam profiles on a trial and error basis. In addition, the maximum length of spring which can be produced is often severely limited.
The encapsulation section relies on the insertion of the fully compressed springs between the sheets of material, most commonly a folded sheet of non-woven fabric, which are then sewn or welded together to produce the individual pocketed springs. Synchronisation of this section is also dependent on mechanical devices such as cams, linkages and a clutch all of which require resetting between products, with resulting loss of productivity and high maintenance costs.
There have now been devised improvements to apparatus and methods for the production of pocketed coil springs which overcome or substantially mitigate the above-mentioned disadvantages.